refactor(@angular/cli): provide default serve target for applications

The `serve` command will now use a default project target and builder
name if the target entry is not explicitly defined. This allows the removal
of additional configuration from an `angular.json` file. If the target is
already present than it will take priority over any default builder behavior.
The default logic will use the appropriate development server builder for
officially supported packages (`@angular/build`/`@angular-devkit/build-angular`).
The `dev-server` builder from these packages will currently assume a `development`
configuration is present within the `build` target. The default behavior may
be expanded in the future to support more arbitrary `build` target configurations.
If there is third-party package usage within the `build` target, the CLI
will attempt to discover a `dev-server` builder within the same package used
by the `build` target. If none is found, no default will be added and the
`serve` command will issue an error when no explicit target is present.

packages/angular/cli/src/commands/serve/cli.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
+import { workspaces } from '@angular-devkit/core';
 import { ArchitectCommandModule } from '../../command-builder/architect-command-module';
 import { CommandModuleImplementation } from '../../command-builder/command-module';
 import { RootCommands } from '../command-config';
@@ -19,4 +20,41 @@ export default class ServeCommandModule
   aliases = RootCommands['serve'].aliases;
   describe = 'Builds and serves your application, rebuilding on file changes.';
   longDescriptionPath?: string | undefined;
+
+  override async findDefaultBuilderName(
+    project: workspaces.ProjectDefinition,
+  ): Promise<string | undefined> {
+    // Only application type projects have a dev server target
+    if (project.extensions['projectType'] !== 'application') {
+      return;
+    }
+
+    const buildTarget = project.targets.get('build');
+    if (!buildTarget) {
+      // No default if there is no build target
+      return;
+    }
+
+    // Provide a default based on the defined builder for the 'build' target
+    switch (buildTarget.builder) {
+      case '@angular-devkit/build-angular:application':
+      case '@angular-devkit/build-angular:browser-esbuild':
+      case '@angular-devkit/build-angular:browser':
+        return '@angular-devkit/build-angular:dev-server';
+      case '@angular/build:application':
+        return '@angular/build:dev-server';
+    }
+
+    // For other builders, attempt to resolve a 'dev-server' builder from the 'build' target package name
+    const [buildPackageName] = buildTarget.builder.split(':', 1);
+    if (buildPackageName) {
+      try {
+        const qualifiedBuilderName = `${buildPackageName}:dev-server`;
+        await this.getArchitectHost().resolveBuilder(qualifiedBuilderName);
+
+        // Use builder if it resolves successfully
+        return qualifiedBuilderName;
+      } catch {}
+    }
+  }
 }